In conventional approaches, cascode technology using MOS transistors can be used to improve the maximum output impedance of an equivalent MOS transistor while the maximum withstand voltage thereof is not increased. A schematic diagram of a conventional cascode current mirror using MOS transistors is shown in FIG. 1. In this example, a voltage at node A can be the sum of the gate-source voltages of MOS transistors 101 and 102. Also, the equivalent output impedance can be increased by applying the cascode MOS transistors, and the output current Iout may not be affected by the output voltage. However, the highest withstand voltage may not be increased with this circuit structure. Therefore, this example may be limited to relatively low voltage applications rather than high voltage applications.
In FIG. 2, a conventional high voltage switching regulator example is shown, and may include driver 202, pulse width modulation (PWM) controller 201, inductor L, switch Q, output diode D0, and output capacitor C0. Here, switch Q may stand with a high voltage, so it may be convenient to select a MOS transistor with a high withstand voltage for switch Q. However, the associated costs may be relatively high. Also, in many applications, the maximum withstand voltages of MOS transistors may be limited by the processes utilized, and may fail to satisfy the needs of a particular application.